Of 420 melee-DPS potency, and over 500 tank potency, since tanks have a damage nerf baked into their unique damage formulas and healers (like casters) have a 30% damage bonus over melee baked in via traits.
That said, it begs a further question:
If tanks insist on having a greater and greater portion of sustain, what is that sustain meant to carry as a reward?
So long as the fight ends by reducing the enemy's HP to 0, all contribution --no matter how indirect-- is ultimately via more quickly reducing the enemy's HP to 0 (even if through a bit more uptime via Expedient, a healer GCD saved, or whatever else). The primary way tank sustain contributes to rDPS outside of not needing to be rezzed is just... more healer offensive GCDs. But you can only push that sustain so far before it becomes redundant, failing to provide any difference to clear time or chance of success.
Why, then, would having excess sustain be in the tank's interest? And similarly, why would it be in the tank's interest to have higher maximum damage than healers, thereby reducing the relative value of proper use of sustain (rewarded through increased healer DPS)?